Temperature dependence of exciton-surface plasmon polariton coupling in Ag, Au, and Al films on In_xGa_1-xN/GaN quantum wells studied with time-resolved cathodoluminescence

The optical properties and coupling of excitons to surface plasmon polaritons (SPPs) in Ag, Au, and Al-coated In_xGa_1-xN/GaN multiple and single quantum wells (SQWs) were probed with time-resolved cathodoluminescence. Excitons were generated in the metal coated SQWs by injecting a pulsed high-energy electron beam through the thin metal films. The Purcell enhancement factor (F_p) was obtained by direct measurement of changes in the temperature-dependent radiative lifetime caused by the SQW exciton-SPP coupling. Three chosen plasmonic metals of Al, Ag, and Au facilitate an interesting comparison of the exciton-SPP coupling for energy ranges in which the SP energy is greater than, approximately equal to, and less than the excitonic transition energy for the InGaN/GaN QW emitter. A modeling of the temperature dependence of the Purcell enhancement factor, F_p, included the effects of ohmic losses of the metals and changes in the dielectric properties due to the temperature dependence of (i) the intraband behavior in the Drude model and (ii) the interband critical point transition energies which involve the d-bands of Au and Ag. We show that an inclusion of both intraband and interband effects is essential when calculating the ω vs k SPP dispersion relation, plasmon density of states (DOS), and the dependence of F_p on frequency and temperature. Moreover, the "back bending" in the SPP dispersion relation when including ohmic losses can cause a finite DOS above ω_sp and lead to a measurable F_p in a limited energy range above ω_sp, which can potentially be exploited in plasmonic devices utilizing Ag and Au.